I see two strains of thought on this throughout the board. Some say it can trick your metabolism or "keep it guessing," and that it makes the diet more doable. And some say it sets them back a day or two, all hard work lost.
I don't know if I could do it- all that work to get white crap out of my system just to negate the ideals of SB for a little boost? Kinda terrifying. If I'd allow myself any kind of cheat, I think it would be not worrying if the restaurant is using butter or not or something. Or not worrying about a creamy sauce once in a blue moon.
Those with experience in trial and error, what say you?

I'd advise against a "cheat day" that includes processed carbs.
Me, too? Cyndi, just pick me up on your way! 